/**
 * Created by dcp on 2018/9/28.
 */


// 寫程式碼實現一個 cut 函式cut(3123123123.123); //3,123,123,123.123
var num=3123123123.123
function cut(num) {
    var arr=num.toString().split('.')

    var t1=arr[0].toString().split('');
    var t2=arr[1].toString();
    var result=[],counter=0;
    for(var i=t1.length-1;i>=0;i--){
        counter++;
        result.unshift(t1[i]);
        if((counter%3)==0&&i!=0)
        {
            result.unshift(',');
        }
    }
    var t3=result.join('')
    var t4=t3+'.'+t2
    return t4



}
console.log(cut(num))